That last bit is the "gray" traffic map. On the "non-gray" map it will also show icons for "events" like accidents, congestion, atypical lane closures, road closures, and the like (assuming you haven't disable any of them). On the "non-gray" map, you get those icons and then grey triangles along the side of congested roadways.

When driving in a trafficy area that's new to me I have the regular map on the left zoomed in, and then the "gray" map on the right zoomed out further. That works well for me to get immediate info on the left side and global info on the right. The right still goes to exit info as needed if a nav route is set.